Now, Schmoes Know reports that a source tells them Fillion will be voicing Cosmo, a psychic dog who is friends with Rocket Raccoon (voiced by Bradley Cooper).

Cosmo is a telepathic Russian canine who is the security chief for the Knowhere space station. In the Marvel comics, he's also a member of the Guardians of the Galaxy.

"Fillion is the perfect man for the job," the site raves. "Not only will the fans perk to attention when they hear Fillion's voice coming out of a psychic dog, but fans of the comic series will smile ear to ear knowing that everything they love of the comic series is being set up (hopefully) for future entries into this universe."

The rumor is totally unconfirmed, though, and director James Gunn threw some cold water on it today when he tweeted:

Still, Fillion seems like a perfect fit for Cosmo (and being a voice role, wouldn't conflict much with his schedule for "Castle"). Whatever role he does end up playing, we're excited that the "Firefly" star is shooting into space once again.